EP0069357A1

EP0069357A1 - Electronic circuit for the control of refrigerating apparatus

Info

Publication number: EP0069357A1
Application number: EP82105889A
Authority: EP
Inventors: Luigi Alluto
Original assignee: Indesit Industria Elettrodomestici Italiana SpA
Current assignee: Indesit Industria Elettrodomestici Italiana SpA
Priority date: 1981-07-08
Filing date: 1982-07-01
Publication date: 1983-01-12
Also published as: IT1144285B; IT8167945A0

Abstract

An electronic delay circuit is described, for refrigerator apparatus which has at least two cooling compartments at different temperatures, each of which is cooled by an evaporator traversed by the refrigerant fluid (one for fresh foods and one for frozen foods), a single compressor, a single condensor and a system of capillary tubes. The said electronic control circuit serves to inhibit attempts to restart the compressor, after it has stopped (for whatever reason) whilst the conditions remain non optimal. More particularly, it avoids attempts to restart the compressor whilst the pressures of the refrigerant fluid in the delivery and induction ducts of the compressor are not in equilibrium and/or if a PTC is used in the starter circuit of the electric motor, with the said PTC still hot. The said electronic control circuit even allows the requirement for a starter capacitor to be eliminated.

This delay is obtained by discharging a capacitor (which is charged during the operating time of the compressor) through a resistor: the charged condition of the capacitor after the compressor has stopped in fact prevents the commutation of a threshold voltage comparator circuit which is responsible for enabling a new start up of the motor of the compressor. The values of the said capacitor and of the charging and discharging resistors are chosen in such a way that the voltage across the said capactor has substantially, instant by instant, the same variation as the pressure in the condenser of the refrigerator circuit.

Description

The present invention relates to an electronic circuit for the control of refrigerating apparatus comprising at least two cooling compartments having different temperatures, each of which is cooled by an evaporator traversed by a refrigerant fluid and one of which is associated with fresh foods and one with frozen foods, a compressor for compressing the refrigerant fluid, a condenser for condensing the refrigerant fluid coming from the compressor, a system of capillary tubing for carrying the refrigerant fluid from the condenser to the evaporators, and in which the two cooling compartments operate substantially independently of one another.
Combined or two-door refrigerators with two cooling compartments, one for fresh foods and one for frozen foods, and a single compressor are known. It is also known that one of the characteristics most desired in this type of apparatus is independent operation of the two cooling compartments. One way of obtaining this object is by putting the evaporators of the two compartments in series or in parallel and by controlling them, by means of solenoid valves, in such a way that the refrigerant fluid circulates in both the evaporators or in only one of these depending on whether it is desired to cool both the compartments or only one of these. Independent control of the two compartments is obtained by means of independent thermostats one fitted in the frozen food compartment and one in the fresh food compartment.
In this way, therefore, both the cooling compartments, independently from one another, can require the compressor to start or stop and this type of operation involves disadvantages in the functioning of the compressor. In fact it is possible that soon after one of the two compartments has reached the desired temperature, and therefore has made the compressor stop, the other compartment requires cooling and therefore would wish to make the compressor start up again. The said compressor, therefore, having just terminated one cycle, has refrigerant fluid at low pressure in the inlet duct and refrigerant fluid at high pressure in the output duct, and given that it is driven by a single phase electric induction motor which has a low starting torque, does not succeed in starting up again. Until now the problem has been resolved by mounting a starting capacitor in series with the starter winding, which by increasing the phase displacement between the currents which flow in the starter and main windings, increases the starting torque of the electric motor by 50-60% thereby allowing the compressor to start up.
But even this solution has its disadvantages, because the said capacitor is of the electrolytic type which involves significant tolerances, has poor reliability (in fact they can blow up rather easily) and finally the cost is not insignificant.
Moreover in motors the main winding of which is controlled by a resistor with a positive temperature coefficient ("PTC"), it is necessary to take account of another problem. When it is first supplied the current flows both in the main winding and in the starter winding, in series with which latter the positive temperature coefficient resistor "PTC" is located. The current by flowing in both the said windings, allows the electric motor to start, but simultaneously heats the "PTC" and this latter experiences a large increase in its resistance and impedes the further passage of current in the starter winding. In this way, after starting, the starter winding is effectively excluded because of the continuous flow of current which maintains the "PTC" hot.
If, however, soon after it has stopped the compressor were to attempt to restart again, the "PTC" would still be hot and the starter circuit would remain always open so that the compressor would not be able to start up again.
The same disadvantage obtains if the compressor should not succeed in starting since, in fact, in this case also, the "PTC" would be heated and subsequent attempts to start would find the starter circuit always open.
Therefore, the object of the present invention is that of overcoming the above mentioned disadvantages and of providing an electronic circuit which functions, after the compressor has stopped, to prevent it from restarting for a time such as to permit the equilibrium conditions of pressure in the inlet and outlet ducts of the compressor itself to be re-established, and to allow the "PTC", if one is used, time to cool completely in such a way that the starting torque of the electric motor, with the pressures balanced, will be sufficient to start the compressor, and in the case of starting with a "PTC", this latter having had time to cool, allows the current to flow in the starter winding.
Further objects of the present invention are those of ensuring that the windings of the electric motor are not subjected to current overloads, and therefore to a high temperature, which could damage them, and to ensure that this electronic circuit will be reliable and of low cost.
To achieve these objects the subject of the present invention is an electronic circuit for the control of refrigerator apparatus comprising at least two cooling compartments at different temperatures, each of which is cooled by an evaporator traversed by a refrigerant fluid and one of which is associated with fresh food and one with frozen foods, a compressor for compressing the refrigerant fluid, a condenser for condensing the refrigerant fluid coming from the compressor, a system of capillary tubing for carrying the refrigerant fluid from the condenser to the evaporators, and in which the operation of the two cooling compartments is substantially independent, characterised by the fact that for ensuring that after the compressor has stopped a predetermined delay occurs before the compressor is started up again, the length of this delay being such as to allow the equilibrium between the pressures of the refrigerant fluid in the delivery duct and the intake duct of the compressor itself to be re-established, there are provided timer means of analogue type which enables a switching circuit to maintain the drive circuit of the compressor motor in an inhibited condition for the duration of the predetermined delay.
Further objects and advantages of the present invention will become clearly apparent from the detailed description which follows and from the attached drawings given purely by way of explanatory and non limitative example, in which:

Figure 1 is a diagram of the electronic control circuit forming the subject of the present invention;
Figure 2 illustrates the driving arrangement for the electric motor of a compressor of a refrigerator, according to the invention;
Figure 3 illustrates the driving arrangement of an electric motor for a compressor, in a second embodiment of the present invention; and
Figure 4 illustrates the variation of the resistance of a resistor of the "PTC" type as a function of time in the cooling phase, such resistor being utilised in the embodiment illustrated in Figure 3.

With reference to Figure 1 there can be seen: a positive supply terminal V_CC to which is connected one terminal of a resistor R ₃ the other terminal of which is connected to the non-inverting input of a threshold comparator CS and a terminal of a resistor R₄ the other terminal of which is earthed. To the inverting input of the threshold comparator CS there are connected one terminal of a resistor R₂, the other terminal of which is earthed, one terminal of a capacitor C₁ the other terminal of which is earthed, and the cathode of a diode D₁ the anode of which is connected to one side of a resistor R₁. The other side of the resistor R₁ is connected to the collector of a PNP transistor Q₁ the emitter of which is connected to the supply V_CC, whilst the base is connected to one side of a resistor R₆ the other side of which is connected to the output Q of a flip flop of the set-reset type indicated FF.
The output of the threshold comparator CS is connected to one side of a resistor R ₅ the other side of which is connected to the supply V_CC, and the set input of the flip flop FF.
To the output Q of the flip flop FF there is also connected one terminal of a resistor R_a the other side of which is connected to the base of an NPN transistor Q₂. The emitter of the transistor Q₂ is connected to earth whilst the collector is connected to one side of a relay coil R_L the other side of which is connected to the supply V_CC, and to the anode of the diodeD₂ the cathode of which is also connected to the supply V_CC. To the reset input of the flip flop FF there are connected one terminal of a resistor R₇ the other terminal of which is earthed, and the output of an OR gate. To the "a" input of the OR gate there is supplied a positive signal for the whole of the time that, for any reason, the switch sensitive to the temperature and/or to the current of the refrigerator on which the electronic control circuit is fitted, interrupts the supply circuit of the electric motor, the input "b" receives a positive signal for the whole of the time that the compressor of the refrigerator is stopped because it has finished a cooling cycle, whilst the input "c" is fed via a capacitor C2 which is connected between this input and the supply V_cc to provide a positive signal whenever the refrigerator is plugged in to the mains.
With reference to Figure 2 where the drive arrangement of the compressor motor of a refrigerator suitable to be associated with the electronic control circuit illustrated in Figure 1 is shown, there can be seen:

a thermostat 3 (mechanical or electronic) of the refrigerator apparatus, which has one contact connected to the network supply terminal 1 and the other contact connected to one terminal of the excitation coil of a starter relay 8 and to a "normally open" contact of the same relay 8. The other terminal of the relay coil 8 is connected to one end of the main winding 6 of a single phase induction motor the other end of which is connected to one end of the starter winding 5 of the same electric motor and to one end of a switch 7 sensitive to current and temperature overloads, the other terminal of which is connected to one of the contacts of the relay RL which is the same as in the electronic control circuit shown in Figure 1, the other contact of which is connected to the other terminal of the network supply 2. The other end of the starter winding 5 is connected to the other contact of the starter relay 8.

For a good understanding of the operation of the electronic control circuit shown in Figure 1 it is necessary also to make reference to the drive arrangement of Figure 2.
Starting from the condition that the compressor of the refrigerator apparatus on which the electronic control circuit is mounted is in operation. In these conditions the output Q of the flip flop FF is low, the transistor Q₂ is non-conducting the relay R_L is not excited and given that it has normally closed contacts it allows the supply to pass to the compressor. The transistor Q₁ on the other hand conducts and the capacitor C₁ is charged through the resistor R₁ and . the diode D₁ with a time constant R₁x C₁ (which in the illustrated embodiment is in the region of 0.18 seconds). When the compressor stops, (because it has terminated a cooling cycle), reset signal reaches the flip flop FF through the logic OR gate. The terminal Q becomes high, the transistor Q₂ conducts, the relay R_L becomes excited and its contacts open preventing the compressor from restarting even if the thermostat should, immediately after a stop, arrive at a new request in this sense. Simultaneously the transistor Q₁ ceases to conduct and the capacitor C₁ starts to discharge through the resistor R2 with a time constant R₂xC₁ (which in the embodiment illustrated is in the region of 50 seconds). The voltage at the inverting input of the threshold comparator CS starts to fall until after a time equal to about 5xR₂xC₁ (in our case about 4 minutes) it reaches the voltage set on the non inverting terminal of the same comparator CS by the voltage divider R₃, R₄. At this point the output of the said threshold comparator CS becomes high and the flip flop FF is sent a set input which makes its output Q go low again turning off the transistor Q₂. This causes closure of the contacts of the relay R_L consequently enabling the motor to start up again if the thermostat circuit requires it.
In conclusion, from the moment that the flip flop FF receives its reset signal (which opens the contacts of the relay R_L) a time of at least about 5xR₂xC₁ seconds must pass before the compressor is enabled to start up again. This charging and discharging of the capacitor C₁ (with the two different time constants) simulates thevariationof the pressure of refrigerant fluid in the condenser of the refrigerator apparatus, and therefore with a suitable choice of the values of R₂ and C₁ a time delay 5xR₂xC₁ which corresponds to the time necessary to re-establish the equilibrium between the pressures in the delivery duct and the induction duct of the compressor can be set. We have said that a reset at the flip flop FF prevents the compressor from starting up again for a time 5xR₂xC₁ so that, to obtain further advantages, it is arranged that such reset can also arrive from the switch 7 sensitive to overloads in the temperature and/ or the current and from the network supply.
The continuous supply V_CC is obtained by means of a supply device connected to the mains such that each time the apparatus is plugged in, a reset signal reaches the flip flop FF through the capacitor C₂ and the OR gate. This means that each time that the plug is inserted into the main supply the electronic circuit, before starting the compressor, checks that the capacitor C₁ is discharged and this gives the advantage that in the case of insertion, removal and re-insertion of the plug (a thing which quite often happens both because of erroneous actions by the user and because of faulty contact) the compressor will not find itself in the critical conditions described above of having to restart immediately after it has stopped. The reset signal which arrives from the switch 7 sensitive to overloads in temperature and/or current via the OR gate, when these are open, serves to ensure that even in the case of a faulty start or an accidental stop for mechanical or thermal reasons, the restarting of the compressor will be delayed by the time 5xR₂xC₁, given that even in this case (without the delay time) the compressor would have to restart immediately after it has stopped.
Moreover, it also serves, in the case where .a positive temperature coefficient resistor is used for starting the electric motor, to give this element time to cool completely, but to better understand the importance of this observation reference will be made to Figures 3 and 4.
In Figure 3, where the same components as in Figure 2 are indicated with the same reference numerals, there can be seen:

a mains supply terminal 1 connected to a thermostat contact 3 (mechanical or electronic) of the refrigerator apparatus. The other contact of the thermostat 3 is connected to one side of a resistor having a positive temperature coefficient (PCT) 4, the other terminal of which is connected to one end of the starter winding 5 of a single phase induction motor, and to one end of the main winding 6 of the same electric motor. The two other ends of the starter winding and the main winding are both connected to one end of a switch 7 sensitive to overloads in the temperature and/or currents, the other end of which is connected to one of the contacts of a relay which is the same as in the electronic delay circuit illustrated in Figure 1; the other contact, in turn, is connected to the other terminal of the mains supply 2.

Finally, in Figure 4 there is shown the variation of the resistance of the PCT as a function of cooling time; that is to say, the instant T=O on the abcissa axis represents the moment when the compressor stops because it has finished a cooling cycle and therefore no more current passes in the PCT. As will be appreciated the graph has been truncated to facilitate the illustration, given that the beginning of the curve is shown to start only after more than a minute from the extinguishing time has passed. The numbers show the values which this resistance assumes in the preceding instants.
As already said, in Figure 2 there is shown an application of the electronic control circuit which solves all the operating problems of the compressor for this type of configuration of starter circuit for the electric motor.
This configuration also permits protection of the integrity of the electric motor to be obtained both in the case of high temperatures of the motor windings and of current overloads in these windings for a time greater than 0.5 seconds.
However, the said configuration has the disadvantage that the starter relay 8 requires calibration for each compressor used and, moreover, the cost of this starter relay 8 is not insignificant. For this reason the adoption of other starting solutions for electric motors which drive compressors have entered into use, which will obviate these disadvantages. One of these uses a resistor with a positive temperature coefficient "PTC" in the starter circuit. The PTC costs less than the relay and moreover works well for all compressors, but also has various disadvantages.
In fact, in this case, it is common practice for the switch 7 sensitive to overloads in the temperature and/ or currents, given that it is traversed only by the operating current, is connected within the motor; with all the problems that this involves, that is to say it must be hermetically sealed against the refrigerant fluid, it must be mounted together with the motor, it must be very reliable, etc.; and moreover this type of switch also has to have dimensions less than those used in the systems of Figure 2 and of the bi-metal type and is primarily sensitive to excess temperature.
Consequently the system of protection is very slow, in fact in the case of extended current overloads (the electric motor is not started or is stopped for some mechanical or thermal impedimenta before the said temperature-sensitive switch opens the circuit it is necessary to wait for the - main winding of the motor to heat by the Joule effect until it reaches a temperature of about 1₄0⁰, and before the circuit is closed again it is necessary to wait for the temperature of the said winding to fall below 100°. All these operations last for about ten minutes, and in the case of a faulty start when there is a need to cool a compartment of the refrigerator this delay is not acceptable.
To resolve the problems of reliability and slowness in the response it would therefore be useful to be able to use a switch of the very quick current sensitive type and to mount it externally of the hermetically sealed container of the electric motor.
This solution too, however, without the electronic control circuit, would not work well in the case of a faulty start because in this case the said current sensitve switch would open and close quickly but the PTC would not have time to cool so that successive attempts to restart the motor would not cause the current to circulate in the starter winding and the compressor would not be able to restart, and this situation would repeat ad infinitum given that the PTC ; always being traversed by current, would remain hot preventing the compressor from restarting.
In conclusion, with a very quick current sensitive switch it is necessary to leave the PTC time to cool completely before making a new attempt to start the compressor.
By looking at Figure 4 , where the variation of the resistance of the PTC as a function of cooling time is plotted, we note how after three minutes the PTC can be considered as practically cold.
To all the above described situations the configuration illustrated in Figure 3 responds, which includes a PTC 4 in the starter circuit, a current sensitive switch 7 mounted externally of the casing of the electric motor and an electronic control circuit not shown, but identical to that illustrated in Figure 1 which controls the contacts of the relay RL. To understand the operation of the said system we start from the condition in which the compressor is operating. In this condition both the contacts of the thermostat 3 and those of the relay R₁ are closed. If the compressor stops because it has finished a cooling cycle the operation is identical to that illustrated with reference to Figure 1. If, on the other hand, the compressor stops accidentally, or else because of a faulty compressor start, the current overload in the windings of the electric motor causes the switch 7 to open which, through the OR gate, sends the reset signal to the flip flop FF.
From this instant, and for a time of 5xR₂xC₁ seconds the contacts with the relay R₂ remain open preventing any attempt to restart the compressor and giving the PTC 4 time to cool completely in such a way that upon a subsequent attempt, finding it cold, the current circulates in the starter winding allowing the compressor to start up again.
In conclusion, the electronic control circuit gives time not only for the pressure of the refrigerant fluid in the delivery and induction ducts of the compressor to regain their equilibrium state, but also gives the PTC time to cool completely so that after a stop or a false start both the pressures and the PTC will be in the best condition for allowing a correct restarting of the compressor.
From the above description the advantages of the electronic delay circuit constituting the .subject of the present invention will be clearly apparent. In particular these include the possibility of making the pressures of the refrigerant fluid regain equilibrium between the delivery and induction ducts of the compressor after it has stopped and before a new start, allowing the use of a starter capacitor to be avoided, the possibility of being able to utilise a PTC in the starter circuit of the electric motor and a switch sensitive to excess temperature and/or to current overload mounted externally of the hermetically sealed container of the electric motor itself with signficiant savings both in the cost of the components and in the labour involved, and the simplicity and reliability of the electronic circuit itself and its low cost.
It is clear that numerous variations of the electronic control circuit described are possible as well as in the systems for its application, such as for example a current overload sensor positioned externally of the hermetically sealed motor container which whenever there is a current overload for a certain time (for example 0.5 seconds) sends a positive signal to the OR gate of the electronic control circuit, and which together with an additional excess temperature sensor positioned in thermal contact with the winding of the motor allows the elimination of the switch sensitive to excess temperature and/or current overloads, or a different manner of obtaining the delay or equivalent circuit solutions without by this departing from the scope of the principles of novelty inherent in the inventive idea.

Claims

1. An electronic circuit for the control of refrigerating apparatus comprising at least two cooling compartments at different temperatures, each of which is cooled by an evaporator traversed by a refrigerant fluid and one of which is associated with the fresh food compartment and one with the frozen food compartment, a compressor for compressing the refrigerant fluid, a condenser for condensing the refrigerant fluid coming from the compressor, a capillary tubing system for carrying the refrigerant fluid from the condenser to the evaporators and having a substantially independent operation of the two cooling compartments, characterised by the fact that in order to ensure a predetermined delay after the compressor has stopped before it is restarted, of a time period such as to allow the re-establishment of the pressure equilibrium of the refrigerant fluid in the delivery and induction ducts of the said compressor there are provided timer means of analogue type which enables a switching circuit to maintain the drive circuit of the motor of the compressor in an inhibited condition for the duration of the said predetermined delay.

2. An electronic circuit for the control of refrigerating apparatus, according to Claim 1, characterised by the fact that the said timer means act via the discharge of an element capable of accumulating energy, which is charged during the normal operation of the compressor, into an element capable of dissipating energy..

3. An electronic circuit for the control of refrigerating apparatus according to Claim 2, characterised by the fact that the said electrical energy accumulation element is a capacitor (C₁), and in that the said electrical energy dissipating element is a first resistor (R₂).

4. An electronic circuit for the control of refrigerating apparatus, according to Claim 3, characterised by the fact that the said capacitor (C₁) is charged through a second resistor (R₁), and in that the values of the said elements and of the said second resistor (R₁ ,C₁ ,R₂) are chosen in such a way that the variation of the voltage across the capacitor substantially represents, instant by instant, the variation of the pressure of the refrigerant fluid in the condenser of the refrigerating apparatus.

5. An electronic circuit for the control of refrigerating apparatus, according to Claim 2, characterised by the fact that the said switching circuit receives, at each stop of the compressor, a signal at one of its inputs which puts it into a condition which produces inhibition to restarting of the compressor until the other of its inputs receives a signal indicating the occurrence of discharge of the said element capable of storing energy which puts it into a condition which permits restarting of the compressor to be enabled.

6. An electronic circuit for the control of refrigerating apparatus, according to Claim 5, characterised by the fact that the said switching circuit includes a threshold voltage comparator circuit (CS) which receives at its non-inverting input a reference voltage derived from a divider circuit formed by two further resistors (R₃,R₄) and at its inverting input the voltage which exists across the terminals of the said element capable of storing energy.

7. An electronic circuit for the control of refrigerating apparatus, according to Claims 5 and 6, characterised by the fact that the said switching circuit also includes a flip flop of the set-reset type (FF) to the set input of which there is connected the output of the said threshold voltage comparator (CS).

8. An electronic circuit for the control of refrigerating apparatus, according to Claim 5, characterised by the fact that it includes a logic OR gate which sends a signal to the input of the said switching circuit when it receives a signal at one or the other of its inputs.

9. An electronic circuit for the control of refrigerating apparatus according to Claim 8, characterised by the fact that it includes a capacitor (C₂) which, each time a voltage is supplied to the electronic circuit, sends a signal to one of the inputs of the said logic OR gate in such a way that in the event of faulty contacts in the supply circuit, or of insertion, removal and reinsertion by the operator of the plug of the apparatus into the electrical supply socket, delays the starting of the compressor to avoid repeated fruitless attempts to start.

1₀. An electronic circuit for the control of refrigerating apparatus, according to Claim 8, characterised by the fact that it includes a switch (7) sensitive to excess temperature and/or to current overloads which while it is operating, opening its contacts, sends a signal to one of the inputs of the said logic OR gate enabling the delay operati.on in the event of false starts or of stoppage of the electric motor of the compressor from mechanical and/or thermal causes.

11. An electronic circuit for the control of refrigerating apparatus, according to Claim 8, characterised by the fact that it includes a current sensor in series with the windings of the electric motor, which, whenever there is a current overload lasting for about 0.5 seconds sends a signal to one of the inputs of the said logic OR gate thereby enabling the delay function.

12. An electronic circuit for the control of refrigerating apparatus, according to Claim 10 and Claim 11, characterised by the fact that it includes a temperature sensor positioned in thermal contact with the said windings of the electric motor, which together with the said current sensor in series with the said windings allows the elimination of the said switch (7) sensitive to excess temperature and/or excess current.

13. An electronic circuit for the control of refrigerating apparatus, according to Claim 1, characterised by the fact that it includes a switch element in the supply circuit of the electric motor for driving the compressor of the refrigerator apparatus itself, controlled from the output of the said switching circuit.

14. An electronic circuit for the control of refrigerator apparatus, according to Claim 13, characterised by the fact that the said switch element is a relay (^R _L).

1₅. An electronic circuit for the control of refrigerator apparatus, according to Claims 2 and 13, characterised by the fact that the opening time of the contacts of the said switch element is determined by the discharge time of the said element capable of storing energy through the said element capable of dissipating it.

16. An electronic circuit for the control of refrigerating apparatus, according to Claim 15, characterised by the fact that the said opening time of thesaidcon- tacts of the switch element and the said discharge time of the said element capable of storing energy through the said element capable of dissipating it are substantially equal.

17. An electronic circuit for the control of refrigerating apparatus, according to Claims 7 and 14, characterised by the fact that the said relay (R_L) is controlled from the output of the said flip flop (FF) through a switching transistor (Q₂).

18. An electronic circuit for the control of ref- rigerathg apparatus, according to Claim 1, characterised by the fact that the electric motor for driving the compressor of the refrigerating apparatus has a starter winding (5) controlled through a PTC(4) , and by the fact that a switch (7) sensitive to excess temperature and/or to excess current is positioned externally of the hermetically sealed casing containing the motor itself and sends a delay request signal to the said switching circuit in the presence of an excess temperature and/or of an excess current.

19. An electronic circuit for the control of refrigerating apparatus, according to Claims 8 and 18, characterised by the fact that the said switch (7) sensitive to excess temperature and/or to excess current opens its contacts when it operates, thereby interrupting the supply to the said electric motor.